This invention relates to an apparatus for controlling the length of movement of a controlled member along a path of repeated operating positions in a numerical control system.
In machine tools of the type controlled by numerical controlled systems, generally described in U.S. Pat. No. 3,657,525 entitled "Direct Feed Rate Control Circuit" and assigned to the same assignee as the present invention, it is often necessary to control accurately the length of movement of a controlled member such as a cutting tool and/or work piece, between repeated operating positions. Operations that can be performed at the operating positions can be punching, drilling, spot-welding, or other operations.
In U.S. Pat. No. 3,657,525, the circuit used to determine when incremental distance along a path of repeated operating positions has been reached is the Vector Approximation Circuit (V.A.C.). The V.A.C. operates by dynamically taking the square root of the sum of the squares of two changing numbers which constitute position change commands per unit of time for the X and Y axis.
The result of these dynamic calculations by the V.A.C. is used to count down a counter that has stored in it the incremental distance between operating positions. The calculations made by the V.A.C. can be inaccurate because of the practical requirement of having to truncate continuing fractions in order that the square root of the sum of two squares can be continually performed as the changing numbers from the function generator are received. When, for example, a V.A.C. is used in a "nibbling operation" (I.E. where a punch press makes successive punches in close proximity to one another, such as every 1/10 of an inch) the accumulated error in measuring the incremental distance between successive operating positions can sometimes cause the last punch of a series of punches to strike a sliver of material resulting in harmful forces on the punching tool. In order to avoid punching slivers, additional circuitry is required.
It is an object of the present invention to improve the accuracy with which the length of movement along a path of repeated operations can be measured.
Another object of the present invention is to provide a new and improved numerically controlled machine adapted for "nibbling" machining operations.
Still another object of the present invention is to provide a new and improved circuit adapted for controlling the length of movement of a control member along a path of repeated operating positions and effective for adapting existing numerically controlled machines equipped with three axes controls for "nibbling" machining operations.